Conventionally, a so-called synchronous rectification type DC-DC converter has been widely used which while driving alternate switching of two semiconductor switching elements connected in series, smoothes a resultantly generated alternating current component by means of an inductor and a capacitor.
For example, a synchronous rectification type DC-DC converter disclosed in Patent Document 1 drives a switching element on a low side to conduct synchronous rectification when an electric load is relatively high, and fails to drive the switching element on the low side and conducts asynchronous rectification (diode rectification) by a diode connected in parallel thereto when the electric load is low. According to such a technique, current conversion efficiency can be improved.